Is Java ArrayList / String / atomic variable reading thread safe?

Question

I\'ve been mulling this over & reading but can find an absolute authoritative answer.

I have several deep data structures made up of objects containing ArrayLists, S

Answer 1

Do NOT use java.util.Vector, use java.util.Collections.unmodifiableXXX() wrapper if they truly are unmodifiable, this will guarantee they won't change, and will enforce that contract. If they are going to be modified, then use java.util.Collections.syncronizedXXX(). But that only guarantees internal thread safety. Making the variables final will also help the compiler/JIT with optimizations.